Multifunctional protective component

ABSTRACT

Subject of the present invention is multifunctional protective component. This new component provides simultaneous protection against voltage strokes and against both high and low frequency disturbances. It is composed of two discrete chip components, namely of multilayer ZnO polycrystalline diode and multilayer ceramic condenser or multilayer self-limiting condenser and multilayer ceramic condenser, which are mutually mechanically connected with non-conductive low-temperature glass (frite), parallel electrical connection between both chips being created with second metallization, and common outer electrodes of newly formed chip. This new component is suitable for surface mounting as well as in terminal leads form.

FIELD OF INVENTION

Subject of the present invention belongs to the field of protectiveelectronic elements, used in safeguarding of other electronic elementsand devices against voltage and current strokes, and against high andlow-frequency disturbances.

TECHNICAL PROBLEM

Miniaturisation and increase of complexity of contemporary electronicelements and systems, as well as their increasingly wider applicationsimultaneously increase their sensitivity to electronic discharge (ESD),voltage excess and strokes and frequency disturbances. These phenomenamay disable normal functioning of separate components, decrease theirstability and reliability and may even destroy them. In this way abovephenomena jeopardise normal functioning of very complex and expensiveelectronic systems Sources of these phenomena may be various. Forinstance the largest source of electrostatic discharge is man itself inthe process of manipulation with electronic devices. Most typical sourceof voltage strokes is lightning, which induces charge in electrical andtelecommunication lines, this charge being transferred through the linesto electronic elements. And some of electronic elements themselves (e.g.electromotor, relay) induce disturbances of various frequencies and emitthem in their closest surrounding. Thus each separate electroniccomponent and its part shall be protected with special components thatprovide such protection. On the other hand this means that disturbanceemission shall be prevented at the source.

Only use of components, with following properties may provide protectionagainst ESD and voltage strokes: non-linear I-U characteristic, shortresponse time and ability to absorb larger amounts of energy. Suchcharacteristics are available in some elements, like Zener diode,multilayer ZnO polycrystalline diode (Varicon), varistor, and condenserswith varistor characteristic or self-limited breakthrough.

The simplest elements for protection against frequency disturbances arecondensers with capacitance up to do 100 nF for high frequencies and incase of lower or radio frequencies with capacitance up to 2000 nF.

Consequently it is clear that in order to protect against all mentionedundesired phenomena, such protective component shall have all requiredproperties: non-linear I-U characteristic, short response time, abilityto absorb larger amount of energy, and adjustable capacitance in rangefrom 10 to 2000 nF. Beside that it must be smaller than any existingsolutions and shall offer surface mounting option with terminal leads.

Subject of this invention, multifunctional component has exactly suchproperties.

STATE OF ART

Beside the most expensive solution, namely use of two discrete elementsin parallel electrical connection e.g. combinations Zenerdiode—condenser or varistor-condenser, there are some other contemporarysolutions one of which is condenser with varistor properties asdescribed in European Patent 418394A. Mentioned condenser is based onSrTiO₃, which provides high value of dielectric constant (ε>20000).Multilayer manufacturing technology provides wide scope of capacitance(10-2000 nF) at relatively small dimensions. However its worst side is,bad varistor characteristic and low value of non-linearity coefficient,soft knee and also high leakage current, high value of breakthroughvoltage temperature coefficient and very narrow range of operatingvoltage. Further more materials for manufacturing such elements andproduction technology are very expensive. In U.S. Pat. No. 5,146,200hybrid bond between multilayer chip varistor and multilayer chipcondenser is disclosed. Physical bond of these two elements is achievedwith gluing and parallel electrical connection is achieved withsoldering.

Components as self-limiting multilayer condenser as shown in U.S. Pat.No. 4,729,058 and multilayer ZnO polycrystalline diode (Varicon diode)have very non-linear I-U characteristic and high self capacitance, whichmay within real dimensions reach up to 100 nF. In that way these twomentioned components provide protection against ESD and voltage strokesand effectively filter high frequency disturbances, but not lowfrequency disturbances.

DESCRIPTION OF INVENTION

New multifunctional component is based on the following facts:

self-limiting multilayer condenser and Varicon diode have suchproperties, which provide effective protection against ESD and voltagestrokes in voltage range from 4 to 150 V

contemporary commercially available chip condensers have very highcapacitance while dimensions are small

both components have similar shape and similar dimensions.

Present invention proves that low temperature scorching providespossibility to create monolith element from two discrete elements, thisnewly created element preserving all unchanged functions of bothdiscrete elements, which are mutually electrically parallel connected innew element.

As mentioned above, two discrete components are used to produce this newcomponent. One of them must provide good ESD protection and goodprotection against voltage strokes. To meet these demands self-limitingcondenser or Varicon diode may be used, both have excellent propertiesof protective component.

Second component only completes already high self capacitance of Varicondiode or self-limiting condenser up to preferred value, which isnecessary for successful protection against high or low frequencydisturbances. For this purposes use of multilayer ceramic condenser ispreferred. Ceramic condenser provides desired capacitance, even up to2000 nF and is manufactured in similar shapes and dimensions as Varicondiode or self-limiting condenser. Both elements to bond shall have equalplanar dimensions (wideness and length) and their largest sides must beeven.

FIG. 1 shows Varicon diode chip (1) and condenser chip (2), eachseparately. As shown in FIG. 1, both components have same shape, equalplanar dimensions, and on their shortest sides outer silver electrodes(3) and (4), which are already formed to allow electrical checking ofboth discrete components. Physical bond between two chips is made insuch manner, that thin layer of suspension (7) is brought on only one oftwo largest area of Varicon diode or condenser, in such way to coverwhole area of the chip between two electrodes (5). Suspension iscomposed from dust of low temperature high resistant glass (frite), withtemperature of glassification between 500° and 800° C., binder andsolvent, which allow glass (frite) as a glass paste, to be placed to thechip surface with printing, brush or in some other manner. Thickness ofthe suspension layer (7) brought to the chip surface is between 10 μmand 500 μm. Immediately after suspension is placed, second unplasteredchip is placed with its larger side on the plastered side of the firstchip in such manner that all edges are even, and their outer electrodes(3) and (4) fall in, and lay one upon another on both sides of thechips, as shown in FIG. 2. Both chips with glass inter layer (7) formsandwich structure. So placed chips are then scorched at temperaturebetween temperature high resistant glass (frite), with temperature ofglassification between 500° and 800° C. Binder and solvent evaporate atlower temperatures so only glass remains between chips (1) in (2). Atcertain temperature glass liquefies and diffuses in bodies of bothcomponents. Depth of diffusion may be controlled via glassificationparameters (time and temperature) to ensure that glass will not diffuseto inner electrodes depth. In certain temperature range glass turns intothin amorphous layer with good mechanical, heat and insulatingproperties, after cooling. Glass layer (7) is very good bound with bothchips, due diffusion into both chip bodies. In that way, with glasslayer (7) very good mechanical bond between both elements is achieved,and the surface between both elements has no porosity. Therefore we maysay, that with glass, one monolith element composed of two discreteelements is created from two discrete elements.

Regardless of the fact that outer electrodes of both chips are inphysical contact, we may still not claim that reliable electricconnection between them is achieved. Therefore so formedcomposition—monolith is repeatedly metallised with Ag or AgPd paste insuch manner, that both smaller sides are plunged to certain depth intoAg or AgPd paste, and uninterrupted outer electrodes (6) of newcomponent are created, both being at the same time in contact with bothouter electrodes of both chips on the inner side. After this paste isscorched at the temperature from 550° to 850° C., reliable electriccontact, and parallel electrical connection between Varicon diode andceramic condenser, as readily shown in FIGS. 3 and 4.

When AgPd is used as second electrode paste, new chip (e.g. protectivemultifunctional protective component) is suitable for surface mounting.

If component with terminal leads is desired, second metallisation willbe performed with Ag paste. So achieved component is placed betweenterminal leads, which will be finally metallurgical and electricalconnected with outer electrodes in soldering process. Additionalmoulding into epoxy resins provides standard shapes of components withterminal leads.

EXAMPLE

Using self-limiting condensers and Varicon diodes on one side andmultilayer condenser on other side, varieties of multifunctionprotective components were made, using above described technique. Someof results are shown in table 1.

TABLE 1 I_(max) C Chip dimensions Un α (8/20 μs) (1 kHz) (mm) (V() 1-10mA (A) (nF)  4 32 50 33 15 29 100 33 3.2 × 2.5 22 28 250 47 27 28 5001000 27 27 1000 680 33 35 2000 470 5.7 × 5.0 33 35 2000 1500Un—breakdown voltage 1 mA α—non-linearity coefficient I_(max) —Higherimpulse current, without consequences for component C—capacitancemeasured at value of 1 kHz

What is claimed is:
 1. A multifunctional protective component to provideprotection against current, voltage, and frequency irregularitiescomprising: a first chip comprising a multiplayer ceramic condenser chiphaving a first end and a second end, each end having an outer electrodeattached thereto; a second chip comprising one of a self-limitingcondenser and a Varicon diode, the second chip having a first end and asecond end, each end having an outer electrode attached thereto; a layerof glass suspension material disposed between the first and secondchips; and a pair of uninterrupted outer electrodes, each uninterruptedouter electrode electrically connecting one of the first chip outerelectrode and one of the second chip outer electrodes thereby providinga parallel electrical connection between the first and second chips;wherein the multifunctional protective component provides simultaneousprotection against current, voltage, and frequency irregularitiesoccurring into the multifunctional protective component through the pairof uninterrupted outer electrodes.
 2. The multifunctional protectivecomponent according to claim 1 wherein the second chip providesnon-linear I-U characteristics, short response time, and an ability toabsorb relatively large amounts of energy.
 3. The multifunctionalprotective component according to claim 1 wherein the second chipcomprises a multilayer ZnO polycrystalline diode.
 4. The multifunctionalprotective component according to claim 1 wherein the first chipprovides a capacitance of up to 100 nF for filtering high frequencydisturbances and up to 2000 nF for filtering low frequency disturbances.5. The multifunctional protective component according to claim 1 whereinthe layer of suspension material is comprised of low temperature, highresistance glass.
 6. The multifunctional protective component accordingto claim 1 wherein the layer of suspension material has a thickness of10 μm to 500 μm.
 7. The multifunctional protective component accordingto claim 1, wherein the first and second chips each have shape andplanar dimensions that are substantially the same with respect to oneanother, and wherein the layer of suspension material is diffused intoboth the first and second chips to create a mechanical bondtherebetween.
 8. The multifunctional protective component according toclaim 1, wherein the pair of uninterrupted outer electrodes are eachcomprised of one of Ag and AgPd and are scorched to obtain the parallelelectrical connection between the first chip and the second chip.
 9. Amultifunctional protective component for providing simultaneousprotection against current, voltage, and frequency disturbancescomprising: a multilayer self-limiting condensor chip having a first endand a second end, each end having an outer electrode attached thereto; amultilayer ceramic condenser chip having a first end and a second end,each end having an outer electrode attached thereto; a layer ofnonconductive glass disposed between and connected to the multilayerself-limiting condensor chip and the multilayer ceramic chip; and a pairof uninterrupted outer electrodes, each uninterrupted outer electrodecovering and electrically contacting one of the outer electrodes of themultilayer self-limiting condensor chip and one of the outer electrodesof the multilayer ceramic condensor chip outer electrodes; wherein aparallel electrical connection between the multilayer self-limitingcondenser chip and the multilayer ceramic condenser chip is achievedwith the pair of uninterrupted outer electrodes, thereby providingprotection of current, voltage, and frequency disturbances through themultifunctional protective component.
 10. The multifunctional protectivecomponent according to claim 9, wherein the multilayer self-limitingcondenser chip and the multilayer ceramic condensor chip each have ashape and planar dimensions that are the same with respect to oneanother, and wherein a layer of nonconductable glass is diffused intoboth the multilayer self-limiting condenser chip and the multilayerceramic condenser chip to create a mechanical bond therebetween.
 11. Themultifunctional protective component according to claim 9, wherein thepair of uninterrupted outer electrodes are each comprised of one of Agand AgPd and are scorched to obtain the parallel electrical connectionbetween the multilayer self-limiting condenser chip and the multilayerceramic condenser chip.